This section provides background information related to the present disclosure which is not necessarily prior art.
To support efficient and flexible transmission, a Long Term Evolution (LTE) release 8 (Rel-8) system needs to support various transmission modulation and coding schemes, including Hybrid Automatic Repeat reQuest (HARP) and link adaptation technologies.
The LTE system obtains a bit sequence with a predetermined length from an encoded bit stream, by puncture or repeating, and this procedure is called rate matching.
In the LTE system, the coding rate of a Turbo encoder used by the traffic channel is 1/3. System information, first parity information, and second parity information output by the Turbo encoder are interleaved respectively, then successively collected by a bit collecting unit.
The interleaved system information is input to a buffer in turn, and then the interleaved first parity information and the interleaved second parity information are input to the buffer alternately, as shown in FIG. 1, which is a schematic diagram illustrating a conventional rate matching buffer.
To support terminals with different capabilities, information in a rate matching buffer shall be shortened, according to a buffer size reported by the terminal, before a base station, e.g. an eNB performs the rate matching for the terminal with lower capability. Total encoded information of a large transport block cannot be stored in the buffer of the terminal with lower capability. FIG. 2 is a schematic diagram illustrating shortened information in a conventional rate matching buffer.
K is a length of information output from the Turbo encoder,
      N    cb    =      min    ⁢                  ⁢          (                        ⌊                                    N              IR                        C                    ⌋                ,        K            )      is a storage size corresponding to a Code block (CB), and the storage size is calculated according to the buffer size reported by the terminal.
C is the number of CBs divided from a Transport Block (TB).
      N    IR    =      ⌊                  N        soft                              K          MIMO                ×                  min          ⁡                      (                                          M                                  DL                  -                  HARQ                                            ,                              M                limit                                      )                                ⌋  
In the above formula, Nsoft is the buffer size reported by the terminal. For the single-code transmission mode, KMIMO=1. For the multi-code transmission mode, KMIMO=2. MDL-HARQ is the maximum number of downlink HARQ processes. For Frequency Division Duplexing (FDD), MDL-HARQ=8. For Time Division Duplexing (TDD), the value of MDL-HARQ is related to TDD uplink-downlink configuration. And Mlimit=8.
In the LTE system, four Redundancy Versions (RVs) are defined for HARQ retransmission, i.e. one CB corresponds to four starting bit positions for transmission. The four RVs are evenly distributed in the buffer, so as to initiate retransmission quickly. According to the RVs configured by the higher layer, a bit selecting unit in the terminal reads bit by bit from the buffer from the starting bit position corresponding to the RV, until the number of read bits reaches a preset value. When the number of read bits does not reach the preset value after a bit in the end of the buffer is read, the bit selecting unit automatically reads bits from the head of the buffer, as shown in FIG. 3. FIG. 3 is a schematic diagram illustrating a conventional redundancy version, where E is the transmission length of the CB.
In a LTE Advanced (LTE-A) system, to support a wider system bandwidth than the LTE system, e.g. 100 MHz, carrier aggregation is proposed. For carrier aggregation, multiple existing spectrums are aggregated together to form a larger bandwidth. FIG. 4 shows the conventional carrier aggregation.
In current standards, each carrier has an independent HARQ process. In the single-code transmission mode, each process includes one TB; in the multi-code transmission mode, each process includes two TBs. One TB can be transmitted via only one carrier. When a base station and a User Equipment (UE) transmit data by multiple carriers, the different carriers transmit the different TBs respectively. When the HARQ function is used, a receiving end will store a decoding failure TB into the buffer, and decode the TB again after combining the TB with the version retransmitted by a sending end.
Currently, in the rate matching process of the LTE-A system, the base station and the terminal may have different buffer sizes.
The size of the CB in a rate matching buffer of the base station is
            N      cb        =          min      (                        ⌊                                    N              IR                        C                    ⌋                ,        K            )        ,where the parameters are the same as the above descriptions.
In the carrier aggregation system, the terminal needs to store more processes, thus the size of one CB in a storage buffer of the terminal is Ncb,UE≦Ncb. However, the size of the CB in a rate de-matching buffer of the terminal is still Ncb, so as to correctly demodulate data.
The existing technologies at least have the following challenges.
Currently, no storage solution is provided when the size of the storage buffer in the terminal is smaller than the size of the rate matching buffer.